Reference may be made to U.S. Pat. Nos. 3,450,119 issued June 17, 1969 to R. E. Sendelbach for an "Air Cleaner Air Inlet Construction" and 3,801,078 issued Apr. 2, 1975 to D. G. Denton for "Thermostatically Controlled Valve Assembly". Both patents disclose air intake duct assemblies for the internal combustion engine air cleaners, the duct having an air inlet for ambient air, a branch exhaust manifold heated air inlet and an air discharge outlet adapted to be coupled to an air cleaner. A flap valve controlled by a temperature sensitive or responsive element responsive to changes in the temperature of the air being discharged from the duct proportions the mix of ambient and heated air passing through the duct.
In both patents the temperature responsive element is a wax or similar pellet that is expandable and contractible in a linear manner. The element is coupled by a driveshaft to the flap valve. The temperature responsive element moves the driveshaft and thereby the flap valve to a heated air inlet fully closed position at a predetermined air temperature. If the temperature rises above the predetermined value, the temperature responsive element overexpands or overtravels. It is necessary to compensate for the overtravel to avoid permanent deformation of the driveshaft or the flap valve. In both the above patents, the override compensation is accomplished by a spring means interposed between the driveshaft and the flap valve.
It is an object of the present invention to utilize an axially loaded, buckling, straight beam driveshaft between the temperature sensitive element and the flap valve, thus eliminating the override coil spring as used in the structure disclosed in U.S. Pat. No. 3,450,119 or the compound wound spring as disclosed in U.S. Pat. No. 3,801,078.